The studies proposed here further test the hypothesis that corticotropin-releasing factor (CRF), the peptide responsible for initiating neuroendocrine stress responses, also functions as a neurotransmitter in the nucleus locus coeruleus (LC) during stress. It is proposed that stressors release CRF from axons innerving the LC, thereby activating these noradrenergic neurons which in turn mediate autonomic and/or behavioral aspects of stress responses. Previous experiments have demonstrated: 1) CRF-immunoreactive (CRF-ir) fibers in LC; 2) LC activation by intracerebroventricular (ICV) or locally applied CRF; and 3) LC activation by a hemodynamic stressor is prevented by microinfusion of a CRF antagonist into LC. The proposed Specific Aims will further test the hypothesis, identify neuronal circuits involved in stress-induced LC activation, and determine the function of LC activation in stress. These aims are: 1) To further characterize the morphology of CRF-ir fibers in LC and to determine the source(s) of these fibers. Laser confocal microscopy, CRG immunohistochemistry, and retrograde tracing will be used; 2) To identify stressors which activate LC, determine whether this activation is mediated by neurotransmitter CRF, and characterize the neuronal circuits involved in this activation. The CRF antagonist, alpha-helical CRF 9- 41 (AHCRF), and dexamethasone will be used to determine whether stress-induced LC activation is due to extrahypophyseal (i.e., neurotransmitter) CRF release. Injections of AHCRF into LC and of GABA into nuclei that are potential sources of CRF innervation will elucidate circuits mediating LC activation; 3) To determine the effects of stress-induced LC activation on autonomic measures, electroencephalographic (EEG) activity, norepinephrine release, and stress-related behaviors. LC discharge, EEG activity, and blood pressure will be recorded in unanesthetized rats. Local LC injection of AHCRF, clonidine, or GABA will be used to assess the role of CRF in the LC and/or of LC activation in arousal or autonomic endpoints of stress. A behavioral index, a proconflict effect, will be similarly evaluated; 4) To determine whether CRF effects on LC discharge, previously demonstrated in rat, extend to monkey. The effects of CRF and hemodynamic stress on LC spontaneous and sensory-evoked discharge will be characterized in monkey. Thus, integrated anatomic, physiologic, and behavioral approaches will reveal some of the mechanisms by which neurotransmitter CRF mediates non-endocrine aspects of stress responses.